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fq_codel: implement L4S style ce_threshold_ect1 marking

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Add TCA_FQ_CODEL_CE_THRESHOLD_ECT1 boolean option to select Low Latency,
Low Loss, Scalable Throughput (L4S) style marking, along with ce_threshold.

If enabled, only packets with ECT(1) can be transformed to CE
if their sojourn time is above the ce_threshold.

Note that this new option does not change rules for codel law.
In particular, if TCA_FQ_CODEL_ECN is left enabled (this is
the default when fq_codel qdisc is created), ECT(0) packets can
still get CE if codel law (as governed by limit/target) decides so.

Section 4.3.b of current draft [1] states:

b.  A scheduler with per-flow queues such as FQ-CoDel or FQ-PIE can
    be used for L4S.  For instance within each queue of an FQ-CoDel
    system, as well as a CoDel AQM, there is typically also ECN
    marking at an immediate (unsmoothed) shallow threshold to support
    use in data centres (see Sec.5.2.7 of [RFC8290]).  This can be
    modified so that the shallow threshold is solely applied to
    ECT(1) packets.  Then if there is a flow of non-ECN or ECT(0)
    packets in the per-flow-queue, the Classic AQM (e.g.  CoDel) is
    applied; while if there is a flow of ECT(1) packets in the queue,
    the shallower (typically sub-millisecond) threshold is applied.

Tested:

tc qd replace dev eth1 root fq_codel ce_threshold_ect1 50usec

netperf ... -t TCP_STREAM -- K dctcp

tc -s -d qd sh dev eth1
qdisc fq_codel 8022: root refcnt 32 limit 10240p flows 1024 quantum 9212 target 5ms ce_threshold_ect1 49us interval 100ms memory_limit 32Mb ecn drop_batch 64
 Sent 14388596616 bytes 9543449 pkt (dropped 0, overlimits 0 requeues 152013)
 backlog 0b 0p requeues 152013
  maxpacket 68130 drop_overlimit 0 new_flow_count 95678 ecn_mark 0 ce_mark 7639
  new_flows_len 0 old_flows_len 0

[1] L4S current draft:
https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-l4s-arch

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
Cc: Tom Henderson <tomh@tomh.org>
Cc: Bob Briscoe <in@bobbriscoe.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2021-10-14 10:59:18 -07:00 • committed by David S. Miller
parent 70e939ddea
commit e72aeb9ee0
5 changed files with 30 additions and 7 deletions
Download patch file Download diff file Expand all files Collapse all files

18
include/net/codel_impl.h
View file

@ -54,6 +54,7 @@ static void codel_params_init(struct codel_params *params)
params->interval = MS2TIME(100);
params->target = MS2TIME(5);
params->ce_threshold = CODEL_DISABLED_THRESHOLD;
params->ce_threshold_ect1 = false;
params->ecn = false;
}
@ -246,9 +247,20 @@ static struct sk_buff *codel_dequeue(void *ctx,
vars->rec_inv_sqrt);
}
end:
if (skb && codel_time_after(vars->ldelay, params->ce_threshold) &&
INET_ECN_set_ce(skb))
stats->ce_mark++;
if (skb && codel_time_after(vars->ldelay, params->ce_threshold)) {
bool set_ce = true;
if (params->ce_threshold_ect1) {
/* Note: if skb_get_dsfield() returns -1, following
* gives INET_ECN_MASK, which is != INET_ECN_ECT_1.
*/
u8 ecn = skb_get_dsfield(skb) & INET_ECN_MASK;
set_ce = (ecn == INET_ECN_ECT_1);
}
if (set_ce && INET_ECN_set_ce(skb))
stats->ce_mark++;
}
return skb;
}